The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Electric motors can convert electric energy to mechanical energy and convert mechanical energy to electrical energy. Known electric motors are connected to an energy storage device thereby enabling the transfer of energy therebetween. Induction machines utilize single-phase or multi-phase power to produce a rotating magnetic field through a series of stators to turn a rotor. The rotating magnetic field induces electrical current through a plurality of conductive bars in the rotor. The electrical current in the conductive bars reacts with the magnetic field produced by the stators to create rotation in the rotor thereby creating mechanical energy in the form of torque.
The stators include a plurality of paired poles that are created from a series of windings and are distributed around the rotor. A common rotor type is referred to as a squirrel-cage rotor. The rotor portion is a laminated structure with bars connected through end rings. The squirrel-cage rotor has a generally cylindrical shape that includes a plurality of conductive bars along a length of a lamination stack at an outer perimeter. The plurality of conductive bars is preferably made of copper due to thermal and conductive properties but other materials, such as aluminum, can be used. The bars in the squirrel-cage are connected at their ends by two end rings. The rotor is assembled by a series of electrically conductive steel laminations through the center of the rotor until it is capped at both ends by shorting rings. The end rings hold the bars and the lamination stack together. The lamination stack is the primary flux-carrying member while the bars carry the current to generate the magnetizing force.
Known rotor fabrication methods include assembling the laminated steel stack with conductor bars on an outer periphery of the rotor and shorting end rings on the ends thereof. This may include placing the laminated steel stack into a casting mold. Molten material is introduced into open spaces formed in the rotor and open spaces between the die cast mold and the laminated steel stack to form the shorting end rings and conductor bars. It is known that oxide inclusions and voids may be formed in the conductor bars and shorting end rings during mold filling of molten material and solidification. The molten material may cool and partially solidify during turbulent flow of the molten material into the plurality of conductor bar grooves due in part to exposure to surface areas of the conductor bar grooves. The partially solidified molten material may impede molten material flow and cause voids, oxide inclusions, and other discontinuities in the conductor bars and the shorting end rings.
Power density output from an electric induction motor correlates to quality of the conductor bars and mass bulk density of the individual conductor bars. It is known that voids formed in the conductor bars and the shorting end rings during fabrication reduce power density output of the electric induction motor. The presence of oxide occlusions and cracks due to hot tearing reduces the electric conductivity of the conductor bars and shorting end rings, thereby reducing the power density output of the motor.
The use of copper material for conductor bars may increase power density and heat transfer characteristics of an induction motor as compared to an induction motor using aluminum conductor bars. The use of aluminum shorting end rings may be cast easier than using a cast copper shorting end ring while providing acceptable heat transfer properties. Known use of copper material for conductor bars and shorting end rings increases manufacturing process times and complexity as compared to aluminum conductor bars and shorting end rings. Known manufacturing processes include casting both the conductor bars and shorting end rings from the same material and welding or brazing conductor bars to shorting end rings.